Motor control system and method for implementing a direct on-off communication control routine

ABSTRACT

A high-efficiency motor control system and method is presented for controlling an electric motor. The system can feature a multi-phase inverter having a logic control device and associated control circuitry, a plurality of floating charge pumps and pump circuitry, a multi-phase bridge having a plurality of power switching devices and a bootstrap capacitor circuit having a floating ground. The floating charge pumps feature grounds electrically coupled to motor phase leads. The bootstrap circuit can feature a floating ground, with a floating voltage being carried across the bootstrap circuit and delivered to the switching devices to produce an indefinite on-time for the switching devices for switching the high-side of a power supply to a load.

FIELD

Embodiments presented herein pertain generally to a control system andmethod for an electric motor and more specifically to a motor controlsystem and method implementing a direct on-off communication controlroutine.

BACKGROUND

Synchronous electric motors such as brushless DC motors andpermanent-magnetic synchronous motors (“PMSM”) or (“PMM”) are commonlyused for high precision applications where careful speed and/or positioncontrol are required. Pulse width modulation (PWM) is a common approachused to control the power supplied to synchronous motors for purposes ofcontrolling the speed and torque of the motor.

Generally, the average value of voltage (and current) fed to theinertial load of a synchronous motor can be controlled through PWM byturning the switch between the power supply and load on and off at afast rate. Typically, PWM switching frequency has to be much higher thanwhat would affect the load. High frequency PWM power control systems canbe easily realizable with semiconductor switches because almost no poweris dissipated by the switch in either the “on” or “off” state. However,during the transitions between “on” and “off” states, both voltage andcurrent are nonzero and thus power is dissipated in the switches. Byquickly changing the state between fully on and fully off (typicallyless than 100 nanoseconds), the power dissipation in the switches can bequite low compared to the power being delivered to the load.

Modern semiconductor switches or transistors such as a MOSFET orinsulated-gate bipolar transistors (IGBTs) are well suited componentsfor high-efficiency controllers. Generally, in such applicationshigh-side switch drivers use something called a “bootstrap” technique toproduce a floating voltage to switch the gate of a semiconductor switchsuch as a MOSFET. This common technique can be cost effective, however,it's very limited to on-time because the bootstrap capacitor dischargesrapidly. Therefore, a PWM signal must be used to turn the MOSFET on andoff thousands of times a second to recharge the bootstrap capacitor. Thedownfall to this is that MOSFETs dissipate the most energy as heat inthe on-off or off-on transition.

This wasted energy is commonly referred to as switching loss. Ingeneral, if heat dissipation isn't properly maintained, the switchinglosses can cascade to the point of complete device failure. Althoughheat sinks can be commonly used to remedy this problem, PWM control canstill be susceptible to higher switching losses which results in lowercontroller efficiency.

Another common circuit used to produce a voltage higher than the busvoltage to drive the gate of a high-side switch is a charge pump. Thebasic charge pump is a circuit that switches back and forth between twocapacitors, charging one while using the other, to maintain a certainvoltage. Due to component limitations with regard to low powercapability and limited output-voltage options, as well as cost concerns,the charge pump is commonly only useful in low voltage applications.

Accordingly, there is a need in the art for a high efficiency motorcontrol system that can be reliable and efficient across a wide range ofmotor loads and speeds. There is additionally a need for such a controlsystem to be cost effective, flexible and robust by being able tominimize heat dissipation and switching loss which can commonlycontribute to device failure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating components of an exemplary motorcontrol system according to embodiments presented herein.

FIG. 2 is a block diagram illustrating components of an exemplaryinverter design according to embodiments presented herein.

FIG. 3 is a circuit diagram illustrating a MOSFET semiconductor switchand exemplary circuitry for switching the high-side of a power supply toa load according to embodiments presented herein.

FIG. 4 is a circuit diagram illustrating exemplary high-side drivercircuitry comprising a bootstrap circuit in combination with a chargepump circuit according to embodiments set forth herein.

FIG. 5 is a graphical view illustrating a comparison of voltagewaveforms between a PWM signal and a continuous on-off communicationsignal routine according to embodiments of the subject invention.

DETAILED DESCRIPTION

While the subject invention is susceptible of embodiment in manydifferent forms, there are shown in the drawings and will be describedherein in detail specific embodiments thereof with the understandingthat the present disclosure is to be considered as an exemplification ofthe principles of the invention and is not intended to limit theinvention to the specific embodiments illustrated.

As presented herein, embodiments of the subject invention are directedto a high-efficiency motor control system for pairing withhigh-efficiency DC motors and permanent-magnetic synchronous motors(“PMSM”) or (“PMM”). Although pulse width modulation (PWM) is agenerally well-known system for controlling an electric motor, suchsystems have several weaknesses, including for example, high switchingloss and lower controller efficiency. Embodiments described hereinrepresent an improvement in motor control design and operation. Asdescribed herein, such embodiments can utilize a direct on-offcommutation routine to control the speed and torque of the motor. As aresult, embodiments disclosed herein are able to produce a higheroverall system efficiency at a wide range of loads and speeds. Theresult is a more cost-effective, flexible, and robust motor controlsystem and method.

Referring now to the drawings and to FIG. 1 in particular, there isshown the basic components of a motor control system 10 according toembodiments presented herein. As illustrated in FIG. 1, the system 10can feature three main stages including: a power supply 12, athree-phase inverter 14 and an electromechanical device 16 driven by thesystem 10. According to embodiments disclosed herein, theelectromechanical device 16 can be electrically coupled to the inverter14 and can comprise a synchronous electric motor such as, for example, aDC motor or permanent-magnetic synchronous motor (“PMSM”) or (“PMM”).The power supply 12 can be electrically coupled, and provide a variablevoltage, to the inverter 14. The power supply 12 can be, for example, ahigh voltage AC to DC buck/boost converter and can consist of multiplestages, including: an electromagnetic interference (EMI) filter, an ACto DC rectification circuit with an active power factor correction (PFC)controller, a buck/boost controller to vary the voltage, and an outputbulk capacitor bank and filter. It will be recognized by persons ofordinary skill in the art that such power supply topology can beimportant to the control method disclosed herein because it can provideprecise, efficient and durable control of the speed and torque of themotor 16.

FIG. 2 illustrates components of an exemplary deign for a three-phaseinverter 14 according to embodiments of the subject invention. Theinverter 14 can generally comprise five stages including: a logiccontrol device 18 (e.g., a microprocessor or microcontroller) andassociated control circuitry, power switching device drivers 20,multiple floating charge pumps 22, a 3-phase bridge 24 consisting of sixpower switching devices or transistors (e.g., metal-oxide-semiconductorfield-effect transistors (“MOSFETs”)) and sensor feedback amplifiers 26for receiving electrical feedback from the motor or load. As illustratedin FIG. 2, the logic control device 18 can be electrically coupled tothe bridge 24 through the power switch drivers 20 and can be separatelycoupled to the feedback amplifiers 26 by a feedback control loop 27. Theinverter 14 can be electrically coupled to motor 16 through the feedbackamplifiers 26 and bridge 24.

Preferably, the inverter 14 can feature three floating charge pumps 22.The floating charge pumps 22 function as independent power supplies withtheir grounds 23 a-23 c referenced to the motor phase leads. It will berecognized by persons of ordinary skill in the art that such design isimportant from the standpoint of using MOSFETs for switching. Inparticular, when using an N-channel MOSFET to switch the positive railor high-side of a power supply to a load, the inverter 14 needs acontrol voltage (also called gate to source voltage) on the order of10-15 volts above the bus voltage.

FIG. 3 illustrates an exemplary circuit diagram of a MOSFETsemiconductor switch 30 according to embodiments presented herein. Forexample, where the bus voltage 32 is 200 volts referenced to ground, thecontrol voltage 34 can be on the order of 215 volts referenced toground, with 15 volts referenced to the load 36. As described above,known techniques for switching the gate of a high-side switch includethe utilizing “bootstrap” technique or a charge pump. Such techniques,however, each individually have weaknesses including, for example, theanticipated onset of heat dissipation and voltage and cost limitations.

FIG. 4 illustrates an improved design for a high-side driver circuit 40according to embodiments of the subject invention where a bootstrapcapacitor circuit 42 can be hybridized with a charge pump circuit 44.According to such embodiments, by taking advantage of the bootstrap's 42floating ground and a constant voltage of the charge pump 22, thehigh-side driver circuit 40 can maintain an indefinite on-time.

As illustrated in FIG. 4, the circuit 40 can also feature a highfrequency oscillator 46 that has a high impedance to ground and cancontrol the charge pump 22 to maintain a constant voltage across thebootstrap capacitor 42. Thus, a variable DC bus voltage 32 can besupplied and delivered to a high-side switch 48 of the inverter 14 and acontrol voltage 34 above the DC bus voltage 32 can be produced anddelivered across the bootstrap capacitor 42 to the high-side switch 48and can switch the high-side of the power supply to a load to maintainan indefinite on-time.

As described above, embodiments set forth herein utilize a direct on-offcontrol technique as opposed to PWM signals to power switches tocommutate the current supplied to the motor. Such direct on-off approachcan run concurrently while the power supply controls the voltage to varythe speed and torque of the motor.

FIG. 5 is a graphical view illustrating a comparison of voltagewaveforms between a PWM signal 50 and a continuous on-off communicationsignal routine 52 according to embodiments of the subject invention. Asillustrated, the PWM signal 50 switches on and off several times percommutation cycle. As it can be expected, PWM control suffers fromhigher switching losses which results in lower controller efficiency.PWM motor drives can achieve high efficiencies, but not as efficient asthe direct on-off approach. With the combination of a variable voltagepower supply, an inverter that is capable of indefinite high-side switchon-time, and a high efficiency DC motor or permanent-magneticsynchronous motor (“PMSM”) or (“PMM”), improved system efficiencies canbe achieved.

From the foregoing, it will be observed that numerous variations andmodifications may be effected without departing from the spirit andscope hereof. It is to be understood that no limitation with respect tothe specific apparatus illustrated herein is intended or should beinferred. It is, of course, intended to cover by the appended claims allsuch modifications as fall within the scope of the claims.

1. A motor control system comprising: a multi-phase inverter having alogic control device and associated control circuitry electricallycoupled to a plurality of power switching drivers; a plurality offloating charge pumps and associated pump circuitry, wherein theplurality of floating charge pumps include respective groundselectrically coupled to respective motor phase leads; a multi-phasebridge including a high-side switching device, wherein the multi-phasebridge is electrically coupled to the plurality of power switchingdrivers and the plurality of floating charge pumps and associated pumpcircuitry; a bootstrap circuit having a floating ground electricallycoupled to the respective grounds of the plurality of floating chargepumps and associated pump circuitry, wherein the bootstrap circuit iselectrically coupled to the plurality of power switching drivers, andwherein a floating control voltage is carried across the bootstrapcircuit and delivered to the high-side switching device to switch ahigh-side of a power supply to a load, and sensor feedback amplifierselectrically coupled to the logic control device by a feedback controlloop.
 2. The motor control system of claim 1 wherein the power supplyincludes a DC power supply converter electrically coupled to themulti-phase inverter, the DC power supply converter comprising anelectromagnetic interface filter, a rectification circuit with a powerfactor correction controller, a controller, and an output bulk capacitorand filter.
 3. The motor control system of claim 1 further comprising anelectromechanical device electrically coupled to the multi-phaseinverter by the respective motor leads.
 4. The motor control system ofclaim 3 wherein the electromechanical device includes at least one of aDC motor and a permanent-magnetic synchronous motor (“PMSM”) or (“PMM”).5. The motor control system of claim 1 wherein the plurality of powerswitching drivers are solid-state semiconductor switches (MOSFETs). 6.The motor control system of claim 1 further comprising a high frequencyoscillator electrically coupled to the plurality of floating chargepumps and associated pump circuitry.
 7. The motor control system ofclaim 1 wherein the plurality of power switching drivers are controlledby the logic control device.
 8. The motor control system of claim 1wherein the logic control device is a microprocessor.
 9. The motorcontrol system of claim 1 wherein the plurality of floating charge pumpsand associated circuitry includes three floating charge pumps.
 10. Anelectric motor control method utilizing a direct on-off communicationroutine comprising: supplying a variable DC bus voltage from a powersupply to a multi-phase inverter, the variable DC bus voltage beingdelivered to a high-side switch of a power switching device of themulti-phase inverter; producing a control voltage, the control voltagebeing above the variable DC bus voltage; delivering the control voltageacross a bootstrap capacitor circuit to the high-side switch, thebootstrap capacitor circuit having a floating ground coupled to a groundof a floating charge pump; controlling the floating charge pump tomaintain the control voltage at a consistent level, the controllingbeing carried out by a high frequency oscillator, and switching thehigh-side switch with the control voltage to couple a high side of thepower supply to a load to maintain an indefinite on-time.
 11. The methodof claim 10 further comprising controlling a speed and torque of a motorelectrically coupled to the multi-phase inverter with an motor leadcoupled to a ground of the high-side switch, the ground of the bootstrapcapacitor circuit, and the ground of the floating charge pump.
 12. Themethod of claim 10 further comprising providing feedback from the loadto a logic control device of the multi-phase inverter.
 13. The method ofclaim 10 wherein the variable DC bus voltage is any voltage levelrequired by the load referenced to ground and the control voltage is thebus voltage plus a voltage in a range between a first minimum switchingthreshold voltage and a first maximum switching voltage allowed by thepower switching device in use referenced to ground and in the range of asecond minimum switching threshold voltage and a second maximumswitching voltage allowed by the power switching device in usereferenced to the load.
 14. A motor control system comprising: amulti-phase inverter having a logic control device and associatedcontrol circuitry electrically coupled to a plurality of power switchingdrivers; a DC power supply converter electrically coupled to themulti-phase inverter, wherein the DC power supply converter comprises anelectromagnetic interface filter, a rectification circuit with a powerfactor correction controller, a controller, and an output bulk capacitorand filter; a plurality of floating charge pumps and associated pumpcircuitry; a high frequency oscillator electrically coupled to theplurality of floating charge pumps and associated pump circuitry; amulti-phase bridge having a plurality of solid-state semiconductor powerswitches including a high-side switch, the multi-phase bridge beingelectrically coupled to the plurality of power switching drivers and theplurality of floating charge pumps and associated pump circuitry; abootstrap circuit having a floating ground, the bootstrap circuitelectrically coupled to the plurality of solid-state semiconductor powerswitches and the plurality of floating charge pumps and associated pumpcircuitry, wherein a floating control voltage is carried across thebootstrap circuit and delivered to the high-side switch to switch ahigh-side of the DC power supply converter to a load, and sensorfeedback amplifiers electrically coupled to the logic control device bya feedback control loop.
 15. The motor control system of claim 14further comprising at least one of a DC motor and a permanent-magneticsynchronous motor (“PMSM”) or (“PMM”) electrically coupled to themulti-phase inverter.
 16. The motor control system of claim 14 whereinthe DC power supply converter delivers a DC bus voltage having a voltagelevel on the order of any voltage required by the load to the high-sideswitch.
 17. The motor control system of claim 16 wherein the floatingcontrol voltage carried across the bootstrap capacitor circuit is equalto the DC bus voltage plus a voltage in a range between a first minimumswitching threshold voltage and a first maximum switching voltageallowed by the plurality of power switching devices in use referenced toground and in a range of a second minimum switching threshold voltageand a second maximum switching voltage referenced to the load.